Like Guillain-Barré syndrome, symptoms may be preceded by a viral illness. Additional symptoms include generalized muscle weakness and respiratory failure. The majority of individuals with Miller Fisher syndrome have a unique antibody that characterizes the disorder. A spinal tap reveals the presence of elevated protein levels. The patient experiences the classical triad of ataxia, opthalmoplegia and areflexia: loss of tendon reflexes and coordination, difficulty walking and standing, vision problems. Also tingling, numbness, dizziness, nausea. Anti-GQ1b antibodies are produced.
The two most common forms can be differentiated with specific tests. In the acute inflammatory demyelinating polyneuropathy (AIDP) form, immune system reactions result in demyelination. It is diagnosed when nerve conduction studies show slowing of nerve conduction suggestive of demyelination in two or more motor nerves. Acute motor axonal neuropathy (AMAN) is diagnosed when nerve conduction studies show a reduction of compound muscle action potential without significant conduction slowing. Testing for serum antibodies to certain nerve components may be useful for confirming the diagnosis of Miller Fisher syndrome (MFS).